The present invention generally relates to television bandwidth reduction techniques and, more particularly, relates to a method and apparatus for enhancing the sharpness of bandwidth compressed pictures.
One approach to bandwidth compression is to limit the luminance bandwidth of two signals to fit in the channel space avilable. In a typical system, 4.5 MHz of the total six megahertz channel is available for luminance information. The rest of the channel is required for sound and channel guardband. The maximum available frequency for luminance for each channel is one-half of 4.5 MHz, or 2.25 MHz. When a sharp cutoff filter is used to limit the luminance of the picture to 2.25 MHz, the picture appears soft. In addition, edges of the picture tend to ring in the filter and cause ghosts at the edge. A slow roll-off filter does not ring, but makes the picture appear softer yet. Equalization can be used to reduce ringing in filters due to improvements in group delay. However, equalizing networks are expensive and take up space and are therefore not desirable in the receiver because both cost and space are at a premium.